Micrel MIC38C44A Bicmos current-mode pwm controller Datasheet

MIC38C42A/43A/44A/45A
Micrel, Inc.
MIC38C42A/43A/44A/45A
BiCMOS Current-Mode PWM Controllers
General Description
Features
The MIC38C4xA are fixed frequency, high performance,
current-mode PWM controllers. Micrel’s BiCMOS devices
are pin compatible with 384x bipolar devices but feature
several improvements.
Undervoltage lockout circuitry allows the ’42 and ’44 versions
to start up at 14.5V and operate down to 9V, and the ’43 and
’45 versions start at 8.4V with operation down to 7.6V. All
versions operate up to 20V.
When compared to bipolar 384x devices operating from a
15V supply, start-up current has been reduced to 50µA
typical and operating current has been reduced to 4.0mA
typical. Decreased output rise and fall times drive larger
MOSFETs, and rail-to-rail output capability increases efficiency, especially at lower supply voltages. The MIC38C4xA
also features a trimmed oscillator discharge current and
bandgap reference.
The MIC38C4xA family is available in 8-pin SOIC and MSOP8 (MM8) package options
• Fast 40ns output rise and 30ns output fall times
• –40°C to +85°C temperature range
meets UC284x specifications
• High-performance, low-power BiCMOS Process
• Ultralow start-up current (100µA typical)
• Low operating current (4mA typical)
• CMOS outputs with rail-to-rail swing
• ≥ 500kHz current-mode operation
• Trimmed 5V bandgap reference
• Pin-for-pin compatible with UC3842/3843/3844/3845
• Trimmed oscillator discharge current
• UVLO with hysteresis
• Low cross-conduction currents
Applications
•
•
•
•
•
•
•
For fast rise and fall times and higher output drive, refer to the
MIC38HC4x.
Current-mode, off-line, switched-mode power supplies
Current-mode, dc-to-dc converters.
Step-down “buck” regulators
Step-up “boost” regulators
Flyback, isolated regulators
Forward converters
Synchronous FET converters
Functional Diagram
VDD
7
5V
Reference
VREF
8
UVLO
†
Oscillator
RT/CT
OUT
4
6
FB
T
Q
S
R
Q
‡
2R
2
2.5V
†
‡
R
COMP
GND
ISNS
1
5
3
MIC38C42A, MIC38C43A (96% max. duty cycle) versions only
MIC38C44A, MIC38C45A (50% max. duty cycle) versions only
MM8 is a trademark of Micrel, Inc.
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
April 2005
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M9999-042205
MIC38C42A/43A/44A/45A
Micrel, Inc.
Ordering Information
Standard
Part Number
Pb-Free
Temperature
Range
Package
MIC38C42ABM
MIC38C42AYM
–40°C to +85°C
8-pin SOIC
MIC38C43ABM
MIC38C43AYM
–40°C to +85°C
8-pin SOIC
MIC38C44ABM
MIC38C44AYM
–40°C to +85°C
8-pin SOIC
MIC38C45ABM
MIC38C45AYM
–40°C to +85°C
8-pin SOIC
MIC38C42ABMM
MIC38C42AYMM
–40°C to +85°C
8-pin MM8™
MIC38C43ABMM
MIC38C43AYMM
–40°C to +85°C
8-pin MM8™
MIC38C44ABMM
MIC38C44AYMM
–40°C to +85°C
8-pin MM8™
MIC38C45ABMM
MIC38C45AYMM
–40°C to +85°C
8-pin MM8™
Refer to the Part Number Cross Reference for a listings of Micrel devices equivalent to UC284x and UC384x devices.
Selection Guide
UVLO Thresholds
M9999-042205
Duty Cycle
Startup 8.4V
Minimum Operating 7.6V
Startup 14.5V
Minimum Operating 9V
0% to 96%
MIC38C43A
MIC38C42A
0% to 50%
MIC38C45A
MIC38C44A
2
April 2005
MIC38C42A/43A/44A/45A
Micrel, Inc.
Pin Configuration
MIC38C4xA
COMP 1
8
VREF
FB 2
7
VDD
ISNS 3
6
OUT
RT/CT 4
5
GND
8-Lead SOIC (M)
8-Lead MM8™ (MM)
Pin Description
Pin Number
Pin Name
1
COMP
Compensation: Connect external compensation network to modify the error
amplifier output.
2
FB
Feedback (Input): Error amplifier input. Feedback is 2.5V at desired output
voltage.
3
ISNS
Current Sense (Input): Current sense comparator input. Connect to current
sensing resistor or current transformer.
4
RT/CT
5
GND
Ground: Combined analog and power ground.
6
OUT
Power Output: Totem-pole output.
7
VDD
Analog Supply (Input): Controller circuitry supply input. Return to analog
ground (AGND).
8
VREF
5V Reference (Output): Connect external RC network.
April 2005
Pin Function
Timing Resistor/Timing Capacitor: Connect external RC network to select
switching frequency.
3
M9999-042205
MIC38C42A/43A/44A/45A
Micrel, Inc.
Absolute Maximum Ratings
Operating Ratings
Supply Voltage (VDD) .................................................... 20V
Switch Supply Voltage (VD) .......................................... 20V
Current Sense Voltage (VISNS) ..................... –0.3V to 5.5V
Feedback Voltage (VFB) ................................ –0.3V to 5.5V
Output Current (IOUT) ................................................... 0.5A
Storage Temperature (TA) ....................... –65°C to +150°C
Junction Temperature (TJ) ........................................ 150°C
Package Thermal Resistance
8-Pin MM8™ (θJA) ............................................. 250°C/W
8-Pin SOIC (θJA) ............................................... 170°C/W
Electrical Characteristics(Note 6)
VDD = 15V, Note 4; RT = 11.0k; CT = 3.3nF; –40°C ≤ TA ≤ 85°C; unless noted
Parameter
Test Conditions
Min
Typ
Max
Units
Output Voltage
TA = 25°C, IO = 1mA
4.90
5.00
5.10
V
Line Regulation
12V ≤ VDD ≤ 18V, IO = 5µA
2
20
mV
Load Regulation
1 ≤ IO ≤ 20mA
1
25
mV
Temp. Stability
Note 1
Total Output Variation
Line, Load, Temp., Note 1
Output Noise Voltage
10Hz ≤ f ≤ 10kHz, TA = 25°C, Note 1
50
Long Term Stability
TA = 125°C, 1000 hrs., Note 1
5
25
mV
–30
–80
–180
mA
47
53
59
kHz
1.0
%
Reference Section
0.2
4.82
Output Short Circuit
mV/°C
5.18
V
µV
Oscillator Section
Initial Accuracy
TA = 25°C, Note 5
Voltage Stability
12 ≤ VDD ≤ 18V
0.2
Temp. Stability
TMIN ≤ TA ≤ TMAX, Note 1
0.04
Clock Ramp
Reset Current
TA = 25°C, VRT/CT = 2V, Note 1
Amplitude
VRT/CT peak to peak
7.7
8.4
%/°C
9.0
1.9
mA
Vp-p
Error Amp Section
Input Voltage
VCOMP = 2.5V
Input Bias Current
VFB = 5.0V
AVOL
2 ≤ VO ≤ 4V
65
90
dB
Unity Gain Bandwidth
Note 1
0.7
1.0
MHz
PSRR
12 ≤ VDD ≤ 18V
60
Output Sink Current
VFB = 2.7V, VCOMP = 1.1V
2
14
mA
Output Source Current
VFB = 2.3V, VCOMP = 5V
–0.3
–1
mA
VOUT High
VFB = 2.3V, RL = 15k to ground
5
6.8
V
VOUT Low
VFB = 2.7V, RL = 15k to VREF
M9999-042205
2.4
2.50
2.58
V
–0.1
–2
µA
dB
0.1
4
1.1
V
April 2005
MIC38C42A/43A/44A/45A
Parameter
Micrel, Inc.
Test Conditions
Min
Typ
Max
Units
Gain
Notes 2, 3
2.85
3.0
3.15
V/V
MaximumThreshold
VCOMP = 5V, Note 2
0.9
1
1.1
V
PSRR
12 ≤ VDD ≤ 18V, Note 2
Current Sense
70
dB
Input Bias Current
–0.1
–2
µA
Delay to Output
120
250
ns
Output
RDS(ON) High
RDS(ON) Low
ISOURCE = 200mA
ISINK = 200mA
20
11
Rise Time
TA = 25°C, CL = 1nF
40
80
ns
Fall Time
TA = 25°C, CL = 1nF
30
60
ns
Ω
Ω
Undervoltage Lockout
Start Threshold
Minimum Operating Voltage
MIC38C42A/4A
13.5
14.5
15.5
V
MIC38C43A/5A
7.8
8.4
9.0
V
MIC38C42A/4A
8
9
10
V
MIC38C43A/5A
7.0
7.6
8.2
V
MIC38C42A/3A
94
96
%
MIC38C44A/5A
46
50
%
Pulse Width Modulator
Maximum Duty Cycle
Minimum Duty Cycle
0
%
Total Standby Current
Start-Up Current
VDD = 13V for MIC38C42A/44A
VDD = 7.5V for MIC38C43A/45A
100
230
µA
Operating Supply Current
VFB = VISNS = 0V
4.0
6.0
mA
Note 1: These parameters, although guaranteed, are not 100% tested in production.
Note 2: Parameter measured at trip point of latch with VEA = 0.
Note 3: Gain defined as:
A =
∆ VPIN1
; 0 ≤ VTH (ISNS ) ≤ 0.8V
VTH (ISNS )
Note 4: Adjust VDD above the start threshold before setting at 15V.
Note 5: Output frequency equals oscillator frequency for the MIC38C42 and MIC38C43. Output frequency for the MIC38C44A, and
MIC38C45A equals one half the oscillator frequency.
Note 6: Specification for packaged product only.
April 2005
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M9999-042205
MIC38C42A/43A/44A/45A
Micrel, Inc.
200pF
470pF
1nF
10
1.8nF
4.7nF
10nF
100
OUTPUT DEAD TIME (%)
RT RESISTANCE (kΩ)
100
MIC38C42/43 Output Dead Time
vs. Oscillator Frequency
VDD = 15V
1.2
1.0
125°C
0.8
0.6
25°C
0.4
-50°C
0
2
4
6
8
ERROR AMPLIFIER OUTPUT (V)
M9999-042205
10
200pF
10nF
470pF
1nF
1
1x104
VREF SHORT CURCUIT CURRENT (mA)
CURRENT SENSE AMP THRESHOLD (V)
Current Sense Amplifier
vs. Error Amplifier Output
0.0
4.7nF
18nF
1
1x104
1x105
5x105
OSCILLATOR FREQUENCY (Hz)
0.2
VDD = 15V
1x105
FREQUENCY (Hz)
1x106
Oscillator Discharge
Current vs. Temperature
9.0
8.8
8.6
8.4
8.2
8.0
7.8
7.6
7.4
VDD = 15V
VOSC = 2V
7.2
7.0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
Short-Circuit Reference
Current vs. Temperature
MIC38C4x
Output Waveform
120
25
100
80
60
40
20
VDD = 15V
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
6
OUTPUT VOLTAGE (V)
Oscillator Frequency
Configuration
OSC. DISCHARGE CURRENT (mA)
Typical Characteristics
20
15
10
5
0
-5
-10
-15
0.0
VD = 15V
CL = 1nF
0.2
0.4
0.6
TIME (µs)
0.8
1.0
April 2005
MIC38C42A/43A/44A/45A
Micrel, Inc.
mended.
When designing high-frequency converters, avoid capacitive
and inductive coupling of the switching waveform into highimpedance circuitry such as the error amplifier, oscillator, and
current sense amplifier. Avoid long printed-circuit traces and
component leads. Locate oscillator and compensation circuitry near the IC. Use high frequency decoupling capacitors
on VREF, and if necessary, on VDD. Return high di/dt currents
directly to their source and use large area ground planes.
Buck Converter
Refer to figure 1. When at least 26V is applied to the input,
C5 is charged through R2 until the voltage VDD is greater than
14.5V (the undervoltage lockout value of the MIC38C42).
Output switching begins when Q1 is turned on by the gate
drive transformer T1, charging the output filter capacitor C3
through L1. D5 supplies a regulated +12V to VDD once the
circuit is running.
Current sense transformer CT1 provides current feedback to
ISNS for current-mode operation and cycle-by-cycle current
limiting. This is more efficient than a high-power sense
resistor and provides the required ground-referenced level
shift.
When Q1 turns off, current flow continues from ground
through D1 and L1 until Q1 is turned on again.
The 100V Schottky diode D1 reduces the forward voltage
drop in the main current path, resulting in higher efficiency
than could be accomplished using an ultra-fast-recovery
diode. R1 and C2 suppress parasitic oscillations from D1.
Using a high-value inductance for L1 and a low-ESR capacitor for C3 permits small capacitance with minimum output
ripple. This inductance value also improves circuit efficiency
by reducing the flux swing in L1.
Application Information
Familiarity with 384x converter designs is assumed.
MIC38C4x Advantages
Start-up Current
Start-up current has been reduced to an ultra-low 50µA
(typical) permitting higher-valued, lower-wattage, start-up
resistors (powers controller during power supply start-up).
The reduced resistor wattage reduces cost and printed circuit
space.
Operating Current
Operating current has been reduced to 4mA compared to
11mA for a typical bipolar controller. The controller runs
cooler and the VDD hold-up capacitance required during
start-up may be reduced.
Output Driver
Complementary internal P- and N-channel MOSFETs produce rail-to-rail output voltages for better performance driving
external power MOSFETs. The driver transistor’s low onresistance and high peak current capability can drive gate
capacitances of greater than 1000pF. The value of output
capacitance which can be driven is determined only by the
rise/fall time requirements. Within the restrictions of output
capacity and controller power dissipation, maximum switching frequency can approach 500kHz.
Design Precautions
When operating near 20V, circuit transients can easily exceed the 20V absolute maximum rating, permanently damaging the controller’s CMOS construction. To reduce transients, use a 0.1µF low-ESR capacitor to next to the controller’s
supply VDD (or VD for ‘-1’ versions) and ground connections.
Film type capacitors, such as Wima MKS2, are recom-
VIN
26V to 40V
R2
68k
D4
1N765B
0.1µF*
D2
M17Z105
1/4W
MKS2
C5
4.7µF
4.7Ω
R1
10
1/2W
C2
1000pF
L1 48µH
31DQ10
D1
C3
3.3µF
C4
0.1µF
0.1µF
6.8k
100k
1
D3
MBR030
VOUT
12V, 2A
Q1
IRF820
CT1
0.22µF
2
3
R4
18
MIC38C42A
COMP VREF
FB
VDD
ISNS
OUT
4
8
5
R5
16k
1N4001
T1
6
RT/CT GND
C7
200pF
D5
7
C8
0.1µF
6.19k
1%
1.62k
1%
*Locate near MIC38C42 supply pins
0.1µF
Figure 1. 500kHz, 25W, Buck Converter
April 2005
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M9999-042205
MIC38C42A/43A/44A/45A
Micrel, Inc.
Magnetic components are carefully chosen for minimal loss
at 500kHz. CT1 and T1 are wound on Magnetics, Inc. P-type
material toroids. L1 is wound on a Siemens N49 EFD core.
Test
Conditions
Line Regulation
VIN = 26V to 80V, IO = 2A
Load Regulation VIN = 48V, IO = 0.2A to 2A
Efficiency
VIN = 48V, IO = 2A
Output Ripple
Symbol
Custom Coil1
ETS2
0.5%
CT1
4923
ETS 92420
0.6%
T1
4924
ETS 92419
90%
L1
4925
ETS 92421
Results
VIN = 48V, IO = 2A (20MHz BW)
1. Custom Coils, Alcester, SD tel: (605) 934-2460
2. Energy Transformation Systems, Inc. tel: (415) 324-4949.
100mV
Synchronous Buck Converter
Refer to figure 2. This MIC38C43 synchronous buck converter uses an MIC5022 half-bridge driver to alternately drive
the PWM switch MOSFET (driven by GATEH, or high-side
output) and a MOSFET which functions as a synchronous
rectifier (driven by the GATEL, or low-side output).
The low-side MOSFET turns on when the high-side MOSFET
is off, allowing current to return from ground. Current flows
through the low-side MOSFET in the source to drain direction.
The on-state voltage drop of the low-side MOSFET is lower
than the forward voltage drop of an equivalent Schottky
rectifier. This lower voltage drop results in higher efficiency.
A sense resistor (5mΩ) is connected to the driver’s high-side
current sense inputs to provide overcurrent protection. Refer
to the MIC5020, MIC5021, and MIC5022 data sheets for
more information.
+12V
VDD
0.1µF
6.8k
300k
4.7nF
MIC38C43A
COMP VREF
4.3k
FB
47k
2200
pF
3.3k
0.1µF
MIC5022
0.15µF
10k
VDD
NC
FLT
VB
NC
EN
GATEL
470µF
25V
NC
ISNS
VOUT
RT/CT
GND
GATEH
IN
SH+
CT
SH–
0.1µF*
MKS2
SMP60N06-14
5mΩ
35µH
VOUT
5V, 8A
1000µF
Low ESR
SL+
GND
10k
SL–
*Locate near the MIC38C43 supply pins.
Figure 2. 100kHz, Synchronous Buck Converter
M9999-042205
8
April 2005
MIC38C42A/43A/44A/45A
Micrel, Inc.
Package Information
0.026 (0.65)
MAX)
PIN 1
0.157 (3.99)
0.150 (3.81)
DIMENSIONS:
INCHES (MM)
0.020 (0.51)
0.013 (0.33)
0.050 (1.27)
TYP
0.064 (1.63)
0.045 (1.14)
45°
0.0098 (0.249)
0.0040 (0.102)
0°–8°
0.197 (5.0)
0.189 (4.8)
0.010 (0.25)
0.007 (0.18)
0.050 (1.27)
0.016 (0.40)
SEATING
PLANE
0.244 (6.20)
0.228 (5.79)
8-Pin SOP (M)
0.199 (5.05)
0.187 (4.74)
0.122 (3.10)
0.112 (2.84)
DIMENSIONS:
INCH (MM)
0.120 (3.05)
0.116 (2.95)
0.036 (0.90)
0.032 (0.81)
0.043 (1.09)
0.038 (0.97)
0.012 (0.30) R
0.012 (0.03)
0.0256 (0.65) TYP
0.008 (0.20)
0.004 (0.10)
5° MAX
0° MIN
0.007 (0.18)
0.005 (0.13)
0.012 (0.03) R
0.039 (0.99)
0.035 (0.89)
0.021 (0.53)
8-Pin MSOP (MM)
MICREL INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL
+ 1 (408) 944-0800
FAX
+ 1 (408) 474-1000
WEB
http://www.micrel.com
This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use.
Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can
reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into
the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s
use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify
Micrel for any damages resulting from such use or sale.
© 2002 Micrel Incorporated
April 2005
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M9999-042205
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